|Aqueous film-forming foams (AFFFs), which contain various classes of per- and polyfluoroalkyl substances (PFAS), have been widely used to extinguish hydrocarbon-fuel fires. Repeated use of AFFFs has led to widespread PFAS contamination. Despite studies on the biotransformation of PFAS in various environmental matrices, very few studies have investigated the biotransformation of PFAS in AFFF-impacted soils, leaving the fate of PFAS in these specific environmental matrices unclear. Recent research suggests that indigenous microbial communities in the environment can transform certain PFAS, but the crucial microbes and enzymes involved in the biotransformation remain poorly understood. Investigating the mechanisms of PFAS biotransformation and the microorganisms involved in the biotransformation is essential to understand the environmental fate of PFAS. Additionally, remediation of sites contaminated with PFAS and co-contaminants poses a significant challenge, yet there has been little focus on addressing this type of challenge.
This dissertation provides an overview of the PFAS problem and research knowledge gaps in Chapter 1, and a comprehensive review of PFAS definition, occurrence, and uses, current and emerging PFAS remediation technologies, microbial biotransformation of perfluoroalkyl acids (PFAA) precursors, and future prospects in Chapter 2. Chapters 3-6 are 4 technical studies. Chapter 3 and 4 describe two aerobic microcosm experiments that investigated biotransformation of representative PFAS in AFFF-impacted soils. Chapter 3 focuses specifically on the aerobic biotransformation of 8:2 fluorotelomer alcohol (FTOH), in two AFFF-contaminated soils. Chapter 4 investigates the ability of a range of sulfonamide- and carboxamide-based precursors in a historically used AFFF formulation to transform in aerobic soil. In Chapter 5, bioinformatic analysis of 16S rRNA amplicon sequencing data from selected PFAS biotransformation microcosm experiments was performed to generate hypotheses about key microbial genera and functional genes involved in the biotransformation of fluorotelomers. Chapter 6 presents a column study that compared the treatment efficiency of a coupled biological and physicochemical system with a single adsorptive system in treating mixed PFAS and chlorinated ethenes. The dissertation concludes with a summary of the major findings from the technical studies and future research recommendations in Chapter 7.